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Received: from 30.74.144.136(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0XEUgVqB_1794298419 cluster:ay36) by smtp.aliyun-inc.com; Tue, 10 Nov 2026 16:13:40 +0800 Message-ID: <9c6eaefd-6d88-4baa-aa9c-b856a1189730@linux.alibaba.com> Date: Tue, 10 Nov 2026 16:13:38 +0800 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/4] mm/huge_memory: don't queue folios when underused splitting is inactive To: Joanne Koong , akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org Cc: baohua@kernel.org, usama.arif@linux.dev, hannes@cmpxchg.org, kas@kernel.org, alex@ghiti.fr, ziy@nvidia.com, liam@infradead.org, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, lance.yang@linux.dev, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, willy@infradead.org, linux-mm@kvack.org References: <20261103212004.1356327-1-joannelkoong@gmail.com> <20261103212004.1356327-3-joannelkoong@gmail.com> From: Baolin Wang In-Reply-To: <20261103212004.1356327-3-joannelkoong@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 51B0B40006 X-Spam-Status: No, score=-19.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS, UNPARSEABLE_RELAY,USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: rhhq1qiec9geggum8an8i9d77x4xxsfe X-Rspam-User: X-HE-Tag: 1794298424-502105 X-HE-Meta: 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 JOsomTEZ dhH146IM4EesxbsFJR3Qid0CiIe5J+HKHPiziy/GZPMxe8KHafKvqrRinDXYiPKTFw3z2vD8BULYbx/w7k8VcaYyB/5jAxII5JPK6S4u7uu+xVpM3of2RrT4181AyvTY/Kg93hahG1WMrqKAbsmE/bO45G4vPnc0dm2FrRxI4zKd/OvGkzEsDCnK2m5pi1j7ySrPBGaFvXmR+QnENr/hj2ApdkGLgm0qQT3qX3rdK9WIvBKurfenlHFnWboy7shTH36InbAiMaamW5NFTa0dtz+8DvGNHdrYBgF3rtbBRXBKxMOWQfEyHddqEHgotOA3O9Mldmg48gcnVXy0Jn/ACuSxIysw0+55cGF/RbYSKLiisCZ7UxdrK2fHU4X2qzO2zB5kSWn7OrkXD0IPmP1ekAXsJHwiaPMfP6fds7CDRU6APh3m7On10Y9Podj47U3UIh6huMKciGCvLe1Y= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 11/4/26 5:20 AM, Joanne Koong wrote: > Every anonymous PMD-sized folio is put on the deferred split queue when > it is first mapped, so that the shrinker can find it under memory > pressure and split it if it turns out to be mostly zero-filled. > > With the default khugepaged/max_ptes_none this is wasted work. The > default is HPAGE_PMD_NR - 1, which tells thp_underused() that any number > of zero-filled pages is tolerable, which means the shrinker will never > split any of these folios for being underused. They take the list_lru > lock at fault time, inflate the object count the shrinker reports, and > are then walked and dropped when they're first scanned. > > Skip the queueing when khugepaged/max_ptes_none is at its maximum, and > factor that check out into thp_underused_never() so that > deferred_split_folio() and thp_underused() share it. Since the default > is the maximum, out of the box no folio is queued for underused > splitting at all, PMD-sized ones included. Partially mapped folios are > still queued as before. > > This also matters for a subsequent patch that adds anonymous mTHP folios > to the deferred split list, as it keeps systems running the default from > paying for that on every anonymous fault. > > Please note that the queue has always been best-effort. A folio that was > queued before khugepaged/max_ptes_none is lowered gets dropped from the > queue by the first scan that finds it's not underused, so changing the > sysctl has never retroactively applied to folios that were already > scanned. Requeueing eligible folios when the sysctl changes will be > addressed in a separate patch. > > Suggested-by: Johannes Weiner > Suggested-by: David Hildenbrand > Signed-off-by: Joanne Koong > --- Reviewed-by: Baolin Wang